MA_Dahlias I mulch every year with straw, and there are definitely seeds that sprout. To be honest, I’m not sure what kind of straw, but it does look an awful lot like what you have there. Two thoughts on this.
1). When I have the straw start growing, I simply grab it by the handful, pull it up, and lay it out on the surface of the rest of the straw. Voila! Bonus straw! It takes a while to get to the point of going to seed, so you don’t really have to stay on top of it quite as much as other weeds.
2). (For future reference) I find that purchasing my bales in the fall (I use them for Halloween and Thanksgiving porch decor) and then throwing them in the garden to sit all winter through the freeze/thaw cycles tends to cut down on the seeds sprouting in spring/summer. Plus the straw gets all nice and matted together so it doesn’t slip/blow around.